Breeding male green turtles, Chelonia mydas, at any one courtship area in the southern Great Barrier Reef mate with females that will nest on rookeries spread throughout the region. In comparison with the breeding females from the same breeding unit, the males are smaller in curved carapace length, and a higher proportion of males remigrate for additional breeding seasons at 1-2-year intervals. Like the adult females, adult males are slow-growing, averaging 0.046 cm year-1. Each male appears to display a fidelity to a particular courtship area, to which it returns in successive breeding migrations. At the conclusion of the courtship period, the males disperse to widely scattered feeding areas.

Feeding-ground captures of green (Chelonia mydas) and loggerhead (Caretta caretta) turtles tagged while nesting at eastern Australian rookeries over a 21-year period are summarised. These turtles which nest in the Great Barrier Reef region range widely throughout the Arafura and Coral seas. The tag recoveries include many from turtles that live in neighbouring countries and migrate to breed in Australia. The breeding female shows a high fidelity to her home feeding ground as well as to her nesting beach. Most recaptures of the green turtles occurred during hunting for food by indigenous people while most recaptures of loggerhead turtles were incidental captures in commercial fishing activities. Migratory behaviour, imprinting and navigation are discussed.

Juvenile loggerhead turtles (Caretta caretta)

Worldwide declines of marine turtle populations have forced a need for sound conservation policies to prevent their extinction. Loggerhead turtles, Caretta caretta, are declining rapidly at eastern Australian nesting beaches, which are visited by females from all feeding areas for the stock. In some feeding areas of eastern Australia, loggerheads have been protected from deleterious anthropogenic effects. Using long-term mark-recapture data from one such protected group of turtles feeding on Heron Island Reef, Queensland, we created a matrix model to analyse loggerhead demography. We also produced a model for the females nesting at Mon Repos, Queensland, a major rookery where the annual nesting population has declined at rates approaching 8% per year. As indicated by a similar model for loggerheads in the USA, our models predicted that small declines in annual survival rates of adult and subadult loggerheads can have a profound impact on population dynamics. A loss of only a few hundred subadult and adult females each year could lead to extinction of the eastern Australian loggerheads in less than a century. Survival in the first year of life is relatively less important in these long-lived and slow-maturing animals. At Mon Repos, nesting female survival is apparently so low that even beach protection efforts resulting in 90% hatchling emergence success would not prevent population decline. Our research suggests that continued mortality pressure on subadult and adult turtles in their dispersed feeding areas of eastern and northern Australia is a major threat to the eastern Australian loggerhead turtle population. Measures that protect adult and subadult loggerhead turtles should be supported, including the use of turtle excluder devices (TEDs) on prawn trawls.

Low-density nesting by hawksbill turtles at Campbell I., Torres Strait, is described. The average female measured 83.2 cm in carapace length, weighed 51.6 kg and laid three clutches per season with a renesting interval of 14.7 days. The average clutch contained 131.8 eggs, mean egg weight was 26 g and mean diameter was 3.6 cm. Hatchling weight was 14.3 g, mean period to emergence was 55 days. Varanid predation is described. Scute variation of adults and hatchlings is summarized.